1. Field of the Invention
This invention relates to an optical pickup of an optical disc device.
2. Description of the Related Art
In the past, there have been widely diffused optical discs such as Compact Disc (CD) and Digital Versatile Disc (DVD) which use red laser light. On the other hand, so as to meet the demand to increase the recording density and enlarge the storage size, next-generation optical discs such as Blu-ray Disc (registered trademark) using blue laser light of 405 nm in wavelength are being diffused. Accordingly, an optical disc device that is adapted to use three kinds of discs or CD, DVD, Blu-ray Disc (also referred to as BD, hereinafter) is being developed.
In an optical pickup to deal with the plural kinds of discs used in such an optical disc device, in case of employing a configuration in which laser light of three kinds of wavelengths corresponding to the CD, DVD, and BD is irradiated to an objective lens using the identical optical system, the optimum optical magnifying power corresponding to the respective formats of the CD, DVD, and BD is not realized.
Accordingly, there is suggested an optical pickup having an optical system provided with two collimator lenses and two objective lenses which have different focal distances (for example, refer to Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2006-24333).
FIG. 1 shows a schematic view of an optical pickup 1 of this configuration, which includes a two-wavelength laser diode 2 that irradiates laser light of 405 nm in wavelength or laser light of 660 nm in wavelength as an optical beam for BD or an optical beam for DVD respectively, a single-wavelength laser diode 3 that irradiates laser light of 780 nm in wavelength as an optical beam for CD, a BD objective lens 12 that converges an optical beam for BD to output thus converged beam to an optical disc 100, and a DVD/CD objective lens 13 that converges an optical beam for DVD or an optical beam for CD to output thus converged beam to the optical disc 100.
The optical pickup 1 further includes a first collimator lens 4 that sets an optical beam for BD or an optical beam for DVD output from the two-wavelength laser diode 2 to a parallel beam to output the resulting beam to a first beam splitter 6. On the other hand, the optical pickup 1 further includes a second collimator lens 5 that sets an optical beam for CD output from the single-wavelength laser diode 3 to a parallel beam to output the resulting beam to the first beam splitter 6.
The first beam splitter 6 reflects an optical beam for BD or an optical beam for DVD at a right angle according to the wavelength thereof, while transmits an optical beam for CD according to the wavelength thereof, and makes the optical beam input to a polarization beam splitter 7. The polarization beam splitter 7 transmits an optical beam for BD, DVD, or CD according to the polarization direction thereof, and makes the optical beam input to a second beam splitter 8.
The second beam splitter 8 reflects an optical beam for BD at a right angle according to the wavelength thereof, and makes the optical beam input to the BD objective lens 12 through a quarter wavelength plate 10, while transmits an optical beam for DVD or an optical beam for CD according to the wavelength thereof, and makes the optical beam input to the DVD/CD objective lens 13 through a upturning mirror 9 and a quarter wavelength plate 11.
The BD objective lens 12 condenses an optical beam for BD to output thus condensed beam to the recording surface of the optical disc 100, and receives a reflected optical beam for BD which is reflected by the recording surface to make the beam input to the polarization beam splitter 7 through the quarter wavelength plate 10 and second beam splitter 8. On the other hand, the DVD/CD objective lens 13 condenses an optical beam for DVD or an optical beam for CD to output thus condensed beam to the recording surface of the optical disc 100, and receives a reflected optical beam for DVD or a reflected optical beam for CD which is reflected by the recording surface to make the beam input to the polarization beam splitter 7 through the quarter wavelength plate 11, upturning mirror 9, and second beam splitter 8.
The polarization beam splitter 7 reflects a reflected optical beam for BD, a reflected optical beam for DVD, or a reflected optical beam for CD according to the polarization direction thereof, and makes the optical beam input to an adjustment lens 14. Then, the adjustment lens 14 condenses a reflected optical beam for BD, a reflected optical beam for DVD, or a reflected optical beam for CD to output thus condensed beam to a light receiving element 15.
FIG. 2 shows a schematic view of an optical pickup 20 of another configuration, in which parts or components similar to those in FIG. 1 are indicated with the same reference numerals.
The optical pickup 20, which is different from the optical pickup 1 shown in FIG. 1, includes a collimator lens 25 that is in shared use for an optical beam for BD, DVD, or CD.
The optical pickup 20 includes a first polarization beam splitter 21 that reflects an optical beam for BD or an optical beam for DVD irradiated from the two-wavelength laser diode 2 at a right angle, and makes the optical beam input to a second polarization beam splitter 22. On the other hand, a half mirror 23 reflects an optical beam for CD irradiated from the single-wavelength laser diode 3, and makes the optical beam input to the second polarization beam splitter 22 through the first polarization beam splitter 21.
The second polarization beam splitter 22 reflects part of an optical beam for BD, an optical beam for DVD, or an optical beam for CD, and makes the part of optical beam input to a light receiving element 24 for a laser power monitor, while transmits the other part of optical beam to make the beam input to the collimator lens 25.
The collimator lens 25 sets an input optical beam for BD, optical beam for DVD, or optical beam for CD to a parallel beam to output the resulting beam to the beam splitter 8.
The beam splitter 8 reflects an optical beam for BD at a right angle according to the wavelength thereof, and makes the optical beam input to the BD objective lens 12, while transmits an optical beam for DVD or an optical beam for CD according to the wavelength thereof, and makes the optical beam input to the DVD/CD objective lens 13 through the upturning mirror 9.
The BD objective lens 12 condenses an optical beam for BD to output thus condensed beam to the recording surface of the optical disc 100, and receives a reflected optical beam for BD which is reflected by the recording surface to make the beam input to the collimator lens 25 through the beam splitter 8. On the other hand, the DVD/CD objective lens 13 condenses an optical beam for DVD or an optical beam for CD to output thus condensed beam to the recording surface of the optical disc 100, and receives a reflected optical beam for DVD or a reflected optical beam for CD which is reflected by the recording surface to make the beam input to the collimator lens 25 through the upturning mirror 9 and beam splitter 8.
The collimator lens 25 sets a reflected optical beam for BD, reflected optical beam for DVD, or reflected optical beam for CD to a converged beam to make the resulting beam input to the second polarization beam splitter 22. The second polarization beam splitter 22 reflects a reflected optical beam for BD, and makes the optical beam input to a BD light receiving element 26 through the adjustment lens 14. Furthermore, the second polarization beam splitter 22 transmits a reflected optical beam for DVD or a reflected optical beam for CD, and makes the optical beam input to a DVD/CD light receiving element 27 through the first polarization beam splitter 21 and half mirror 23.
The collimator lens 25 is attached to a lens holder 29 that is driven back and forth by a motor 28 in the optical axis direction. Accordingly, the optical pickup 20 can compensate the spherical aberration with respect to BD or DVD by shifting the collimator lens 25 in the optical axis direction.